Heat exchangers



United States Patent HEAT EXCHANGERS Howard R. Dammond, Great Neck,N.Y., assignor to Landam Products Corporation, Great Neck, N.Y., acorporation of New York Application July 30, 1957, Serial No. 675,174

7 Claims. (Cl. 219-39) This invention relates to heat exchangers andmore particularly to electrically-energized liquid heaters of thethrough-flow or instantaneous type.

In the design of through-flow heaters for liquids, particularlyfaucet-type Water heaters, in which the heating element takes the formof an electrical resistance, it is in most cases necessary for safetyand simplicity to provide control action whereby current flows only whenliquid is flowing in the unit. In order, however, to insure that therenot be a significant time lag in the appearance of heated liquid at theoutput, the total volume of liquid in the unit at any given instantshould be kept small. Also in those cases in which the heat exchanger isto be used as a faucet attachment for providing hot Water at a coldwater tap, weight, size and reliability of the unit are importantfactors, as is the ability of the unit to keep itself free of foreignmatter over a long life.

Accordingly, it is one object of the present invention to provide animproved heat exchanger of the throughfiow type for heating liquids.Other objects of the invention are to provide a through-flow type heatexchanger for liquids which is electrically efficient, self-purging, andsafe for use on faucets.

In accordance with the invention, a heat exchanger is provided with aliquid flow path in the form of a generally toroidal space betweenconcentrically-arranged inner and outer tubes, the innermost tube ofwhich carries internally any electrical resistance heater element. Thetube assembly is preferably formed into coils, with the center areawithin the coils containing control elements. An inlet fitting isattached to the outer tubular member adjacent one end thereof and anoutlet fitting to the member adjacent the other end, communication withthe toroidal space being established through suitable apertures in theouter tube. Turbulent flow in the toroidal space is utilized to effectefiicient heat transfer, to scavenge the heat-exchanging surfaces and togenerate back pressure within the system.

The back pressure generated within the system by the passage of liquidtherethrough is sensed adjacent the inlet end of the exchanger tooperate a control element in the form of a pressure-responsive switchfor closing the electrical power circuit to the heater element, theswitch automatically opening to break the circuit when the source ofliquid under pressure is cut off as by closing the Water tap on theupstream end of the unit, for example. A thermal switch can be includedin the unit in the form of a fuse assembly connected in series in theelectrical circuit and physically joined in a thermal coupling to asection of the outer tube. The fuse assembly is preferably receivedwithin the coils for greater sensitivity. The coil assembly with itsseveral control elements is mounted in a casing, preferably in anelectrically insulating potting compound for protection against damageto the unit and shock to the users.

A representative embodiment of the invention is-described below, havingreference to the accompanying drawings, in which:

2,879,372 Patented Mar. 24, 1959 Figure 1 is a view in side elevation,partly in vertical section, of a heat exchanger unit of the type adaptedto be attached to a water tap for instantaneous heating;

Figure 2 is a top view, partly in horizontal section, taken on the line2-2 of Figure 1, looking in the direction of the arrows;

Figure 3 is an enlarged view partly in section, of a control element inthe heat exchanger for controlling the flow of electrical current; and

Figure 4 is an enlarged perspective view of a second control elementcomprising a fuse assembly normally mounted within the heating coils ofthe unit.

Referring to the drawing, the invention is illustrated as embodied in aheat exchanger unit indicated generally by the numeral 10 of the typeadapted to be attached to the nozzle of a cold water faucet F forproviding a flow of heated water from its outlet or discharge nozzle 11,the heating of the water occurring automatically as a function of theWater flow through the unit. The unit 10 includes a casing 12 formed inits upper surface with an opening 13 to accommodate a faucet adapter 14.

; The lower surface consists of a thin disc 49 of insulatingrepresenting the liquid flow path. The inner tubular member is notnecessarily centered within the outer tubular member at any given pointalong the length of the coil. Thus, While the cross-sectional area ofthe flow path is constant along its length, the configuration variesrandomly, thereby augmenting the desired turbulent fiow therein. Thetubular members 17 and 18 are preferably formed of metal tubing which iscorrosion resistant. At the upper end of the coil 16 the inner tubularmember extends beyond the end of the outer tubular member 18 in anextension 13a. Similarly, at the lower end 18b of the inner tubularmember, there is a protrusion from the outer tubular member. At theupper and lower ends of the outer tubular member 17 seals 17a and 17b,preferably formed of silver solder, close the toroidal space 19.

An inlet fitting 20, including an internal chamber or conduit 20a, issecured to the coil 16 close to its upper end as by soldering orbrazing, for example, and within the fitting the outer tubular member 17is formed with a milled slot 21 (Figure 2) connecting the channel ofinlet with the toroidal space 19. The discharge nozzle or outlet 11 issimilarly joined to the coil 16 adjacent its lower end, withcommunication between the outlet 11 and the toroidal space alsooccurring through an openingin the outer tubular member. In thisfashion, water from the faucet F flows through the inlet fitting 20 intothe toroidal space 19, around the several coils of the unit 16 and outof the outlet 11.

The liquid flowing through the toroidal path is heated by means of anelectrical resistance heater element 22 passing through the center ofthe inner tubular member 18, the heater element 22 being connected atits upper end to a conductor lead 22a and. at its lower end to aconductor lead 22b. The space between the heater element 22 and themetal Walls of the tubular member 18 is filled with a ceramic insulator23 which affords a heatconducting path to the metal walls which surroundit.

The electrical circuit to energize the resistance heater 22 includes anelectrical supply conduit or cord 24,

terminating in a cord cap 25 to beplugged into the mains, and controlelements including a fuse assembly 26 and a pressure-operated switch 27.The control elements are mounted within the coils of the heat exchangerunit 16.

One conductor 24a of the electrical supply cord 24 is connected to aterminal 29b of the control switch assembly 27, the other terminal 29aof which is connected to the conductor lead 22b of the resistanceheater. The other conductor lead 22a of the resistance heater isconnected to a terminal 28b of the fuse assembly 26, the other terminal28a of which is connected to the conductor 24b of the electrical supplycord 24 to complete the circuit. The fuse assembly 26 includes, as bestseen in Figure 4, an insulating plate 30 having mounted at its ends apair of fuse clip elements 31a and 31b joined respectively to theterminals 28a and 28b. A cartridge fuse 32 is received in the clips 31aand 3112, the fuse preferably comprising a thermal fuse including afuseable element under spring pressure to insure its parting to open thecircuit at the time of melting. Between its ends the insulating plate 30carries a third, relatively-wide clip element 310 which embraces theinsulating glass center of the fuse 32. The clip element 31c is joinedby 'a heavy metal screw 33 to a metal mounting block 34 which is in turnsecured in thermal conducting relationship, as by brazing, to one of theinner coils of the heat-exchanging coil 16. In this fashion, the supportfor the fuse assembly 26 also forms a thermal conducting path by meansof which heat from the coil is conducted to the fuse element 32. Heatingin the coil beyond a predetermined value will therefore open theelectrical circuit.

The control switch assembly 27, as best seen in Figure 3, includesnormally-open, snap-type contacts 35 (indicated diagrammatically) and apush-type actuator 36 which extends out of the switch housing. Securedto the housing 37 around the actuator 36 is a plate 38 formed with acentral aperture 39 in which is received a discshaped actuating element40. Overlying the aperture 39 and the surface of the disc element 40 isan impervious, flexible diaphragm 41 which can take the form of a thindisc of heat and water-resistant Neoprene. The switch housing, togetherwith the plate 38 and the diaphragm 41, is secured to a mounting plate42 attached to the inlet fitting 20 to communicate with the chamber 20a.Thus, the inlet water path is placed in direct communication with thediaphragm 41. In operation, the pressure, representing the backpressure, of water in the chamber 20a works on the diaphragm 41 todepress the actuator 36 to close the contacts 35 to energize the heatingelement 22 of the heat exchanger unit 16.

The heat-exchanging coil 16, including the several control elementsassociated therewith, is preferably potted or sealed within the housing12 by means of a water impervious electrical insulator such as epoxyplastic resin 48. The housing can be partially potted, as illustrated,or fully potted. The outlet 11 includes a diffuser 43 taking the form ofa cup element having a series of holes in its underside to disperse theoutput flow and fitted over a depending tubular element 44 whichconnects to the toroidal flow path of the heat-exchanging coil. Thediifuser 43 is slipped onto the element 44 over an O-ring 45 andoperates to form the discharge of heater water into a plurality ofstreams while at the same time affording a pressure relief valve in theevent of clogging by virtue of its ability to slide off of the fitting44 under the controlled frictional force of the O-ring 45. The adapter14 by means of which the unit attaches to a water faucet includes arubber sleeve v46, water-tightly secured to a threaded bushing as bymolding, for example. The threaded bushing is screwed onto the inletfitting 20. In operation, the sleeve 46 is fitted over the nozzle of thefaucet and tightened in place by a screw-operated tension band 47. Itwill be understood that other adapter fittings can be used in accordancewith the requirements of particular units,

In a preferred embodiment of the invention the heatexchanging coil 16included an outer tubular member 17 of .375 inch outside diameter and awall thickness of .02 inch, and an inner tubular member of .290 inchoutside diameter. Both members were formed of type 321 stainless steel,and the length was about 26 inches formed into a coil of 2.375 inchesinside diameter after the two straight lengths were joined one withinthe other. An electrical resistance heater of 8 ohms was used to providea wattage of about 1700 to 1800 for heating the water. Using a switch inwhich the contacts are opened by a pressure on the actuator of 9 to 1302s., a .500 inch diameter opening was used for the aperture 39 in theplate 38 to achieve operation when the back pressure at the inlet was inthe range of 3 to 6 psi. The unit will operate with conventionalpressures in the supply line of 30 to 70 p.s.i., with the faucet valvebeing used to control the flow, as described below.

In operation, with the unit mounted on a closed water faucet,electricity does not flow in the heating element. When the water isturned on at the faucet, the water flows into the toroidal space 19 ofthe coil 16 and around the coils to the outlet 11. The relatively smallclearances between the inner and outer tubular members 17 and 18 resultsin a back pressure at the inlet fitting 20 which closes the contacts 35of the control switch assembly 27 to energize the electrical resistanceheater 22, the element remaining energized as long as the flow of watercontinues above a predetermined minimum. By controlling the flow ofwater at the faucet, the temperature of the outlet water can becontrolled, higher pressures or a wide-open faucet providing a rapidflow of warm water and lower pressures arising from a partially closedfaucet providing a slower flow of hot water. As the temperatureapproaches critically hot values, however, the back pressure drops belowthe minimum value to operate the control switch and the power is cutoff. The water passing through the toroidal space in intimate contactwith the metal surface of the inner tubular member 18 will be heated.Because of the relatively small volume of water in the unit at any giventime, heated water is obtained quickly. The efiiciency of the heattransfer to the flowing water is augmented by the turbulent flowtherein. The turbulence of the flow and the high velocity has ascavenging effect which serves to purge the critical space of scaleimpurities or the like. To achieve the desired flow characteristics inthe toroidal space 19, it is not necessary that the inner tubular memberbe centered within the outer tubular member. Rather, the random spacingof the two members serves to achieve increased turbulence which improvesthe heating efficiency. Overheating will melt the fuse to open thecircuit.

While the invention has been described above having reference to apreferred embodiment thereof, it will be understood that it can takevarious other forms and arrangements and should not, therefore, beregarded as limited except as defined by the following claims.

I claim:

1. In a water heater, an outer tubular member, an inner tubular membermounted in the outer member to define a generally toroidal spacetherebetween, liquid inlet means adjacent one end of the toroidal space,outlet means adjacent the other end, said toroidal space affording animpedance to water passage therethrough to establish turbulent fiow andto generate a back pressure therein, electrical resistance heater meansin the inner tubular member, whereby the inner tubular member becomes aheat exchanging surface enveloped by water on all sides, switch meansconnected in series with the resistance heater, and means responsive toliquid pressure in the toroidal space generated by the flow of watertherethrough to actuate said switch to energize the resistance heater,whereby the impedance to flow established by the presence of theexchanging surface within the outer member both generates back pressureto efiect energization of said resistance heater and establishesturbulent flow to enhance the transfer of heat from the heat exchangingsurface to the water.

2. In a water heater, an outer tubular member, an inner tubular membermounted in the outer member to define a generally toroidal spacetherebetween, liquid inlet means adjacent one end of the toroidal space,outlet means adjacent the other end, said toroidal space affording animpedance to water passage therethrough to establish turbulent flow andto generate a back pressure therein, electrical resistance heater meansin the inner tubular member, switch means connected in series with theresistance heater, means responsive to the liquid pressure in thetoroidal space generated by the flow of water therethrough to actuatethe switch to energize the resistance heater, and thermal-responsivemeans thermally coupled to the outer tubular member and connected inseries in the electrical circuit to the resistance heater, thethermal-responsive means opening the electrical circuit when thetemperature of the tubular member exceeds a predetermined value.

3. A heater as set forth in claim 1, said outlet means comprising adepending tubular discharge conduit communicating with the toroidalspace, a cup-shaped cap fitted on the conduit and including a pluralityof waterdispersing openings therein, and a resilient O-ring interposedbetween the conduit and the cup to impose a predetermined frictionalholding force thereon.

4. A heater as set forth in claim 1, said means responsive to pressurein the toroidal space being in com munication with the toroidal spaceadjacent the inlet means.

5. A heater as set forth in claim 1, said means responsive to pressurein the toroidal space comprising a flexible, impervious diaphragm incommunication on one side with the toroidal space, a support membermovably mounted beneath the diaphragm to urge the diaphragm out of itsnormal plane toward the source of pressure, and a switch actuatorinterposed between the support memher and said switch means.

6. A heater as set forth in claim 2, said inner and outer tubularmembers comprising metal tubes taking the configuration of a helicalcoil, said thermal-responsive means comprising a metal block aflixed tothe outer tubular member and extending in cantilever fashion into thecenter of the coil, a metal clip member attached to the block, and anelectrical fuse element having a pair of terminals and an insulatingbody portion, the body portion being received in said clip member.

7. A heater as set forth in claim 6, including a casing for the coiledtubular members, and an electrically insulating potting compound fillingthe spaces among the coils and between the coils and the casing.

References Cited in the file of this patent UNITED STATES PATENTS1,438,445 Loubiere Dec. 12, 1922 1,759,774 Andriulli May 20, 19301,920,284 Wells Aug. 1, 1933 2,588,314 Wicks Mar. 4, 1952

